package main

import (
	"fmt"
	"image"
	"image/color"
	"image/gif"
	"io"
	"log"
	"math"
	"math/rand"
	"net/http"
	"strconv"
	"time"
)

var palette = []color.Color{color.White, color.Black}

const (
	whiteIndex = 0 // 画板中的第一种颜色
	blackIndex = 1 // 画板中的下一种颜色
)

func init() {
	rand.Seed(time.Now().UTC().UnixNano())
}

const (
	// cycles  = 5     // 完整的x振荡器变化的个数
	res     = 0.001 // 角度分辨率
	size    = 100   // 图像画布包含[-size, size]
	nframes = 64    // 动画中的帧数
	delay   = 8     // 以10ms为单位的帧间延迟
)

var cycles float64

func main() {
	handler := func(w http.ResponseWriter, r *http.Request) {
		if err := r.ParseForm(); err != nil {
			log.Print(err)
		}
		for k, v := range r.Form {
			if k == "cycles" {
				x, _ := strconv.Atoi(v[0]) // 忽略错误
				cycles = float64(x)
			}
		}

		lissajous(w)
	}
	http.HandleFunc("/", handler)
	log.Fatal(http.ListenAndServe("localhost:8000", nil))
	return
}

func lissajous(out io.Writer) {	
	fmt.Print("cycles: ", cycles)
	if cycles <= 0 {
		cycles = 5
		fmt.Print(". Set Default: 5")
	}
	fmt.Println()

	freq := rand.Float64() * 3.0 // y振荡器的相对频率
	anim := gif.GIF{LoopCount: nframes}
	phase := 0.0 // phase differencs
	for i := 0; i < nframes; i++ {
		rect := image.Rect(0, 0, 2*size+1, 2*size+1)
		img := image.NewPaletted(rect, palette)
		for t := 0.0; t < cycles*2*math.Pi; t += res {
			x := math.Sin(t)
			y := math.Sin(t*freq + phase)
			img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5), blackIndex)
		}
		phase += 0.1
		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}
	gif.EncodeAll(out, &anim) // 注意：忽略编码错误
}
